In semiconductor elements, it is possible to use buried, doped layers so as to connect vertically oriented components from “below.” It is also possible to provide a buried layer for isolation or shielding purposes. In all cases, such a buried layer needs a contact with the surface, which is undertaken via a low-ohmic doping that extends to the buried layer.
Additionally to this, isolating trenches are needed in semiconductor elements, so as to isolate component structures from one another. Thus, for example, there is a need to isolate a buried layer that is correlated with a first component structure from a second semiconductor structure that is not in direct electrical connection with it; this may also be, for example, a buried layer. Such an isolating trench then requires a depth that surpasses that of the buried layer, so as to create a secure isolation with a high breakdown voltage.
From published US Patent Application US 2004/0018704A1, a method is known, with which a low-ohmic connection of one component surface can be produced from a component surface to a buried layer and simultaneously, an electric isolation between two sections of a buried layer. To this end, a trench to the buried layer is first etched and then a doping substance is introduced into the trench walls; this substance then creates low-ohmic contact structures there. In the following step, the trench is further etched to a desired depth required for the isolation, and the inside walls are finally coated with a dielectric.
Furthermore, the electric contacting of buried layers via so-called sinker dopings is known, which are created at a certain depth of the semiconductor substrate and by diffusion produce the low-ohmic zone for the contacting of the buried layer with the surface.
The contacting of a buried layer via a sinker contact has the disadvantage that while driving the doping to the desired depth, simultaneously a lateral diffusion takes place and the lateral expansion of the sinker contact is thus unnecessarily increased and an unnecessarily large amount of surface is taken up, which can no longer be used for other component structures.